Migrating ESL 9595 tape library slot licenses

Scenario: Customer own two Extended Tape Libraries ESL 9595. One library own 595 slot license (Prod) and the other owns 400 slot licenses (DR). Customer decommissioning the "Prod" TL and moving some of the tape drives from the "Prod" TL to "DR" TL (yes they are of same type, so no issue there).

Issue: Customer wants to know if it is possible for them to migrate the slot licenses from the "Prod" TL to "DR" TL or they have to procure more licenses ?